With the constant development of communication technologies, 2G, 3G, and 4G communication systems are currently coexisting, and both device suppliers and network operators expect a communication device capable of operating in multiple frequency bands and in multiple operating modes to thereby lower a device production cost, and a network operating and maintenance cost. Furthermore the communication device is also required to operate efficiently in the multiple frequency bands and in the multiple operating modes from the perspectives of saving energy, reducing emission, and eco-friendly communication. There are inevitable bandwidth and efficient design challenges to a power amplifier which is such a component in the communication device that has the most seriously constricted operating bandwidth and consumes significant energy.
The existing high efficient power amplifiers are generally embodied in the Doherty circuit structure for their high efficiency, but the Doherty circuit structure thereof includes a λ/4 impedance conversion line which is such a narrowband component that results in a limited available bandwidth of the traditional Doherty structure. An inverted Doherty circuit structure is an efficient solution to a power amplifier for a wider bandwidth, and respective components in the power amplifier are required to match therewith, but not all the components may operate therewith. The existing gallium nitride, GaN, components, particularly components consuming high power, generally can not technically operate in the inverted Doherty circuit structure, so the GaN components still have to operate in the traditional Doherty circuit structure to be improved, and accordingly the Doherty circuit structure needs to be redesigned for an improved bandwidth thereof.